Preparation of alpha,alpha-dimethylbenzyl alcohol



United States Patent Ofiice Patented ,f,;;

Delaware No Drawing. Filed Dec. 9, 1964, Ser. No. 417,199 7 Claims. (Cl. 260-618) This application constitutes a continuation-in-part of my application for Letters Patent, Serial No. 49,848, filed August 16, 1960, now abandoned.

This invention relates to a process involving the oxidation of cumene and more particularly it relates to a method for converting cumene to a product containing a high yield of u,a-dimethylbenzyl alcohol but containing substantially no a,a-dirnethylbenzyl hydroperoxide and acetophenone.

It is known that cumene may be oxidized to reaction products containing preponderant amounts of either a,a-dimethylbenzyl hydroperoxide or u,a-dimethylbenzyl alcohol. Either one of these products may be obtained in higher yield in relation to the other by suitable selection of reaction conditions. For example, it has been shown that the formation of a,a-dimethylbenzyl alcohol is favored by the use of heavy metal oxidation catalysts and by comparatively high temperatures. However, even under such conditions, substantial amounts of the hydroperoxide and acetophenone have been formed,

A method for the preparation of high purity 06,0L-dlmethylbenzyl alcohol in high yield is needed. The alcohol is useful, for example, as an intermediate in the production of u-methylstyrene and bis(a,a-dimethylbenzyl) peroxide. In the preparation of both of these compounds acetophenone should be absent, and a,a-dimethylbenzyl hydroperoxide should not be present in the preparation of a-methylstyrene. Various methods have been devised to prevent or remove the hydroperoxide and the acetophenone contents of an oxidate containing a,a-dimethylbenzyl alcohol.

It was found that by oxidizing cumene to a low conversion to oxygenated product, it was possible to keep the ketone content comparatively low in relation to the total crude oxidate. However, the amount of ketone was still appreciable in relation to the total oxygenated products recovered by distillation of the crude oxidate to remove unreacted cumene. Furthermore, under these conditions of low conversion, the amount of hydroperoxide formed was considerable, and it became necessary to remove the hydroperoxide by chemical treatment involving an additional step. For example, it is known to reduce the hydroperoxide with hydrogen catalytically or through use of sodium sulfite or sodium sulfide. It also was found possible to effect reaction between the hydroperoxide and unreacted cumene by heating in the presence of certain catalytic materials.

All of these procedures are disadvantageous, however, in that they result in a sacrifice in alcohol yield or necessitate utilization of additional processing steps. It long has been desired that a simplified process could be devised for converting cumene to a reaction product containing a, x-dimethylbenzyl alcohol as the principal oxidation product, with essentially no a,u-dimethylbenzyl hydroperoxide and the minimum in amount of acetophenne Now in accordance with this invention, such a process has been discovered and it comprises three essential steps:

(1) a carefully controlled oxidation, (2) a digestion step carried out on the oxidate under an oxygen partial pressure which is insufficient to efiect formation of any further substantial amounts of primary oxidation products, namely, the hydroperoxide and the alcohol, and (3) the step of removing some of the water from the oxidate prior to or during the digestion step. Using batch oxidation, the steps may be combined to provide a unitary operation.

The oxidation is carried out by intimately contacting cumene in liquid phase with oxygen under either atmospheric or higher pressures, or with air under pressures greater than atmospheric, at temperatures of about 90 to about 120 C. in the presence of aqueous solutions of sodium hydroxide ranging in concentration from about 45% to about by weight of sodium hydroxide. Upon completion of the oxidation step, the resulting reaction mixture is digested by heating it at an elevated temperature, preferably the same temperature as used during the oxidation, until the residual hydroperoxide content has been reduced to less than about 1%. During the digestion, it is necessary that the concentration of sodium hydroxide be such that reduction of the hydroperoxide is efficiently and substantially carried out. The proper concentration of sodium hydroxide is provided by removal of some of the water from the oxidate prior to or during the digestion step. Also, it is preferable to provide conditions during the digestion and water-removal steps whereby the amount of acetophenone is considerably decreased.

Having thus described the invention, the following examples are offered as specific embodiments thereof. All parts and percentages are by weight unless otherwise indicated.

Example 1 A stainless steel autoclave equipped with a reflux condenser and a stirrer and designed for high pressure oxidations was charged with 90 parts of cumene (refractive index at 20 C., 1.4910; purity, 95-97%) and 12.6 parts of sodium hydroxide in the form of a 45.2% queous sodium hydroxide solution. Stirring was begun, and air was introduced, with the pressure reaching psig. Steam was turned on in the coils surrounding the autoclave, and the temperature was raised to 70 C., then gradually to C. over a period of one hour. Air was passed through the reaction mixture at a rate of 0.17 cubic feet/minute/kilogram of cumene,

Oxidation at the 90 C. temperature was carried out for 11.0 hours, at which time the oxidate had a specific gravity of about 0.940 and contained about 5% of ct,oc-dlmethylbenzyl hydroperoxide. At this point, the pressure on the system was released, but all other reaction conditions were maintained. The oxidate then was digested for a period of 9.5 hours and during this time, by means of a water trap in the reflux system, 13 parts of water was removed from the reaction system. The cumene also occurring in the distillate was returned, after separation from the water, to the autoclave.

The reaction mixture resulting from the digestion step was washed twice with water to remove substantially all of the sodium hydroxide, each water wash amounting to about 30 parts. There was obtained 76.2 parts of washed product, and upon analysis it was found to have a specific gravity of 0.954 and to contain 66.5% u,a-dimethylbenzyl alcohol, 0.1% a,a-dimethylbenzyl hydroperoxide and 03.4% cumene. The Weight of cumene consumed accordmgly was 64.5 parts, and the percent cumene reacted was 71.8. The amount of sodium hydroxide charged was thus 0.195 gram per gram of cumene reacted In comparison, when the reaction conditions of the oxidation step of the above process were essentially duplicated, but the digestion and water-removal steps were omitted, there was obtained an oxidate which, after water washing, had a specific gravity of 0.952 and analyzed for 59% alcohol, 4% hydroperoxide and 37% cumene. This shows the need for the digestion and water-removal steps of the process in producing an oxidate containing less than 1% of hydroperoxide.

Example 2 In contrast to the exhaustive, batch-type of oxidation in the preceding example, cumene was oxidized continuously and to a comparatively low percent cumene reacted level in the present example. The equipment was composed of a glass oxidation vessel fitted with a reflux condenser, thermometer, high-speed stirrer, internal cooling coil and external heating. Reactants were fed to the top of the oxidizer and product was withdrawn from the bottom.

The cumene used in this example was 98100% pure, the sodium hydroxide was in the form of a 50% aqueous solution, the oxidant was oxygen and the pressure was atmospheric. The oxidizer was charged with a eumene oxidate from a previous run, and stirring and introduction of oxygen were begun. The temperature of the reaction mixture was brought to 110 C., and then the cumene, the aqueous caustic and oxygen were introduced, and product removed, at the desired rates to provide a steady state of oxidation. In the present instance, the introduction of the 50% aqueous sodium hydroxide was at a rate sufiicient to provide 4.9 parts of sodium hydroxide/ 100 parts of cumene, and the oxygen flow was such as to provide an off-gas rate which was about equal to oxygen consumption.

After steady operation was established, the oxidation was run for a period of 1.64 hours, the average rate of oxidation being 12.9%/hour. The per cent cumene reacted was 21.1. The amount of sodium hydroxide charged was 0.23 gram per gram of cumene reacted A sample of the oxidate, after being washed with 0.5 its weight of water at room temperature, was analyzed and found to contain 76% cumene, 17.6% alcohol, 3.1% hydroperoxide, 0.8% acetophenone and 0.6% biS(oz,oc-dimethylbenzyl) peroxide. The reaction yield for the alcohol was calculated to be 77.4%.

A portion of the unwashed oxidate in an amount of 171.9 parts was charged to a glass reaction vessel fitted with a condenser, stirrer and thermometer, and heated to 125 C. A total of 3.7 parts of distillate was removed, this constituting 1.8 parts of water and 1.9 parts of cumene. The oxidate was then stirred for one hour, after which the hydroperoxide concentration was 0.2%. The digested product, minus the samples removed for hydroperoxide determination, amounted to 155.3 parts, and this was washed with water in the same way as the oxidate, yielding 138.5 parts of washed product. Analysis showed that the product contained 76% cumene, 24% alcohol, 0.2% hydroperoxide, 0.6% acetophenone and 0.6% bis(u,a-dimethylbenzyl) peroxide. The reaction yield for the alcohol was 88.5%.

A comparable oxidation except for use of 1.7 parts sodium hydroxide/ 100 parts of cumene was carried to a percent cumene reacted level of 19.0, and gave a washed oxidate analyzing for 78% cumene, 14.3% alcohol, 4.9% hydroperoxide, 0.7% acetophenone and 0.5% peroxide. Digestion of the oxidate with reduction in the hydroperoxide content was accomplished in about one-third of the time used in the first run under this example, showing an advantage for using a lower level in amount of sodium hydroxide. In the present run the amount of sodium hydroxide charged was 0.09 gram per gram of cumene reacted Example 3 Cumene was oxidized as in the first run under Example 2 except to use a temperature of C. and a steady state reaction period of 3.03 hours. The percent cumene reacted was 24.3 (0.20 gram sodium hydroxide charged/ gram cumene reacted), and the average oxidation rate was 8% /hour. A sample of the oxidate, after being washed as in Example 2, analyzed for 75% cumene, 21% alcohol (reaction yield, 80.3%), 3.5% hydroperoxide, 0.8% acetophenone and0.3% peroxide. A portion of the unwashed oxidate was digested for 4 hours at 98 C. and was sparged with nitrogen during this period to remove water. The digested product was then washed in the same manner as the oxidate, and the washed product was found to contain 72% cumene, 25.8% alcohol (reaction yield, 89.5%), 0.1% hydroperoxide, 0.5% acetophenone and 0.6% peroxide.

A comparable oxidation in which the concentration of the aqueous sodium hydroxide solution was reduced to 40% resulted in an oxidate of substantially increased hydroperoxide content. Furthermore, water removal from and digestion of the oxidate showed a comparatively low (about one-fourth) rate of disappearance of hydroperoxide content. This finding, plus the indicated operability of aqueous 45% sodium hydroxide in Example 1, establishes the need for charging to the oxidation an aqueous sodium hydroxide having a minimum concentration of about 45%. It also was found that under the conditions of the present example, substantially no oxidation occurred when air at atmospheric pressure was substituted for oxygen.

The process of this invention is dependent upon a combination of certain specific and limited reaction conditions. The process necessarily involves three steps, the first an oxidation, the second a digestion and the third a water removal step. In each step, the conditions specified are essential. In the oxidation, the temperature is between about 90 and about 120 C., the preferred range being about 90 to about 100 C. Below 90 C. the oxidation does not proceed at a satisfactory rate and above C. the yield of a,a-dirnethylbenzyl alcohol decreases with increasing temperature.

A most important factor is the concentration of the aqueous sodium hydroxide solution charged to the process. Below about 45%, the hydroperoxide content increases during the oxidation, and the rate of oxidation decreases. In other words, an aqueous sodium hydroxide concentration below about 45% will not accomplish the objective of high rate of oxidation with minimum hydroperoxide formation. Furthermore, the concentration of the aqueous sodium hydroxide charged has a profound effect on the ease with which the digestion step may be carried out. For example, when 50% sodium hydroxide was charged, the concentration had fallen to about 40% upon completion of the oxidation, but upon removal of water to raise the concentration to 46%, the reduction of hydro-peroxide by digestion took place at an appreciable rate (hydroperoxide half life=20 minutes). How ever, the use of 40% sodium hydroxide with concentration to 44% by water removal after oxidation required a much longer digestion period to effect hydroperoxide reduction (hydroperoxide half life=80 minutes). The minimum concentration of about 45 aqueous sodium hydroxide needed for the oxidation also leads to satisfactory results during the digestion step. Concentrations above about 70% are not practical due to the high freezing points of the solutions and the resulting difficulty of keeping process lines from plugging. Preferred concentrations are in the range of about 45 to about 55%, with 50% being the most preferred concentration value.

The amount of 45% to 70% aqueous sodium hydroxide charged to the oxidation must be sutficient to provide adequate alkalinity in the oxidation and also in the digestion step, in both of which there is a consumption of the sodium hydroxide charged. With 45% aqueous sodium hydroxide, the amount may be from about 2.2 to about 66.7 parts by weight per 100 parts by weight of cumene charged to the oxidation. With 70% aqueous sodium hydroxide, the amount may be from about 1.4 to about 42.9 parts by weight per 100 parts by weight of cumene. The corresponding amounts for 50% aqueous sodium hydroxide are from about 2 to about 60 parts, and for 55% aqueous sodium hydroxide are from about 1.8 to about 54.5 parts by weight per 100 parts by weight of cumene.

In general, for the over-all range of between about 45% and about 70% aqueous sodium hydroxide, an amount of aqueous sodium hydroxide from about to about 45 parts by weight per 100 parts of cumene will provide a high rate of oxidation with minimum hydroperoxide formation, and will enable the reduction of the hydroperoxide in the digestion step to proceed at a satisfactory rate to a substantially low hydroperoxide level. A preferred range is from about 10 to about 30 parts by weight per 100 parts of cumene. By m nimizing hydroperoxide formation, there is less formation of acetophenone due to thermal degradation of the hydroperoxide.

The examples have shown percent cumene reacted values of about 20 to about 70%. However, this range may be between about and about 70%. In an exhaustive oxidation such as that of Example 1, the percent cumene reacted may range from about 50 to about 70, but in continuous oxidations such as those of Examples 2 and 3 it is preferred not to exceed about 40%. Beyond this point, there is a fall-off in rate of oxidation and yield of alcohol. A preferable range is from about to about 40% cumene reacted, with being optimum.

As shown in the examples, either air or oxygen may be used as oxidizing agent. Both are operable under superatmosphen'c pressures, but the rate of oxidation with air is too low at atmospheric pressure. Operable pressures range from about 5 to about 500 p.s.i., but a preferred range is about 60 to about 200 p.s.i., this being particularly applicable to the use of air as oxidant. The temperature and pressure may be readily adjusted to obtain optimum results. The rate of input of the oxidizing agent may be varied depending upon whether oxygen or air is used, and upon the pressure. At pressures of from 50 to 200 p.s.i. for example, the rate of input may be from about 2 to about 200 liters of oxygen per hour per kilogram of cumene. A preferable range is from about 20 to about 60 liters of oxygen per hour per kilogram.

The digestion step of the process of this invention is ordinarily carried out within the same temperature range as that applicable to the oxidation, namely, about 90 to about 120 C., although slightly higher temperatures up to about 140 C. may be used. At temperatures below about 90 C. the rate of reduction of hydroperoxide is too low. It is important during the digestion step that the concentration of the aqueous sodium hydroxide solution be no less than about 45 otherwise the hydroperoxide reduction will not proceed satisfactorily to the final low level desired. A concentration of about 50% is preferred, but the overall operable range is from about 45% to about 70% The time involved during the digestion step will vary depending upon the amount of hydroperoxide in the oxidate, the concentration of the aqueous caustic and the temperature. However, it generally will range from about 30 minutes to about 8 hours, longer times being 6 involved when the amount of water necessarily to be removed is substantial. When the amount of water to be removed is not great, then from about 30 minutes to about 2 hours generally will suffice.

The digestion step is carried out under an oxygen partial pressure which is insufiicient to efiect formation of any further substantial amounts of primary oxidation products. This partial pressure may actually be Zero, but as shown in Example 1, it is desirable when the oxidizing agent is air to continue to pass air at atmospheric pressure (or at a slightly elevated pressure of 510 p.s.i.) through the oxidate while carrying out the digestion. The temperature during such treatment should be between about and about 120 C. This leads to a product low in acetophenone content, the acetophenone being converted to benzoic acid, actually the sodium salt, which is removable from the organic material by water washing.

The step of water removal in accordance with the process of this invention may be carried out prior to or during the digestion step. The water is distilled off from the oxidate, preferably with the help of a stream of gas, as in Examples 1 and 3. The amount of water removed will vary, depending primarily on the amount and concentration of aqueous sodium hydroxide charged to the process. Nevertheless, the amount removed should be sufiicient to provide a concentration of about 45 to about 70% aqueous sodium hydroxide during the digestion step. Furthermore, even in the case of use initially of sodium hydroxide solutions of comparatively high concentration, for example, above 55 it is necessary to remove some of the water of reaction although the actual concentration of the aqueous sodium hydroxide at termination of the oxidation may be about 45% or better. This is based on the observation that as the concentration of the aqueous sodium hydroxide charged to the process is increased, there is an increase in sodium hydroxide consumption and production of water of reaction during the oxidation. Thus, in such cases, there is so much water present that it interferes with efficient reduction of hydroperoxide during the digestion step. Generally, the amount of water removed will be between about 2 and about 20 parts by weight per parts by weight of oxidate. A preferred range is about 5 to about 15 parts of water by weight per 100 parts by weight of oxidate.

The process in accordance with this invention represents a convenient and simple method for obtaining an u,u-dimethylbenzyl alcohol product substantially devoid of a,a-dimethylbenzyl hydroperoxide and acetophenone. The process accomplishes this objective in three steps and all that is then required is the separation of the alcohol from unreacted cumene. This may easily be accomplished by fractional distillation in a packed column.

What I claim and desire to protect by Letters Patent is:

1. The process for converting cumene to a reaction product containing u,tx-dimethylbenzyl alcohol as the principal oxidation product which comprises intimately contacting cumene in liquid phase with an oxidizing agent selected from the group consisting of oxygen and pressurized air at a temperature from about 90 to about C. in the presence of an aqueous solution of sodium hydroxide having a concentration between about 45 and about 70%, until the percent cumene reacted is between about 15 and about 70%, removing from the oxidate at least part of the water existing therein and digesting the oxidate at a temperature from about 90 to about C. under an oxygen partial pressure which is insuflicient to effect formation of any further substantial amounts of primary oxidation products until the residual hydroperoxide content of the oxidate has been reduced to less than about 1%, the concentration of the aqueous sodium hydroxide solution during this digestion step being within the range of about 45% to about 70%.

2. The process of claim 1 wherein the water is removed from the oxidate prior to the digestion step.

3. The process of claim 1 wherein the Water is removed from the oxidate during the digestion step.

4. The process of claim 1 wherein the oxidizing agent is air under a pressure of about 60 to about 200 psi. and wherein air is passed through the oxidate at atmospheric pressure during the digestion step.

5. The process of claim 4 wherein the water is removed from the oxidate during the digestion step.

6. The process of claim 1 wherein the oxidizing agent is oxygen and wherein the water is removed from the oxidate prior to the digestion step.

7. The process of claim 1 wherein the temperature during oxidation is about 90 to about 100 C. and the temperature during digestion is about 90 to about 120 C.

References Cited by the Examiner UNITED STATES PATENTS 2,438,125 3/1948 Lorand et a1 260618 2,548,435 4/1951 Lorand et al 260618 2,687,438 8/1954 Lorand et a1 260-618 2,713,599 7/1955 Lorand 260618 3,009,963 11/1961 Hock et a1 260618 LEON ZITVER, Primary Examiner. 

1. THE PROCESS FOR CONVERTING CUMENE TO A REACTION PRODUCT CONTAINING A,A-DIMETHYLBENZYL ALCOHOL AS THE PRINCIPAL OXIDATION PRODUCT WHICH COMPRISES INTIMATELY CONTACTING CUMENE IN LIQUID PHASE WITH AN OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OF OXYGEN AND PRESSURI IZED AIR AT A TEMPERATURE FROM ABOUT 90* TO ABOUT 120* C. IN THE PRESENCE OF AN AQUEOUS SOLUTION OF SODIUM HYDROXIDE HAVING A CONCENTRATION BETWEEN ABOUT 45% AND ABOUT 70%, UNTIL THE PERCENT CUMENE REACTED IS BETWEEN ABOUT 15 AND ABOVE 70%, REMOVING FROM THE OXIDATE AT LEAST PART OF THE WATER EXISTING THEREIN AND DIGESTING THE OXIDATE AT A TEMPERATURE FROM ABOUT 90* TO ABOUT 140* C. UNDER AN OXYGEN PARTIAL PRESSURE WHICH IS INSUFFICIENT TO EFFECT FORMATION OF ANY FURTHER SUBSTANTIAL AMOUNTS OF PRIMARY OXIDATION PRODUCTS UNTIL THE RESIDUAL HYDROPEROXIDE CONTENT OF THE OXIDATE HAS BEEN REDUCED TO LESS THAN ABOUT 1%, THE CONCENTRATION OF THE AQUEOUS SODIUM HYDROXIDE SOLUTION DURING THIS DIGESTION STEP BEING WITHIN THE RANGE OF ABOUT 45% TO ABOUT 70%. 